brewed a scottish ale w/ the gf on sat, and all went wonderful! but one thing has still been bothering me:

after cooling to about 65F and pitching, mixed, grabbed a sample of the aerated wort, poured into a clear tube, and stuck in the hydrometer, story begins...

first look, 1054, but was a bit foamy on top (1/8"), so I waited some time. looked like 1056. waited more (no foam now) looked like 1057. more time and it's 1059, maybe verging toward 1.060...

has this happened to anyone else? the temp couldn't have varied more than 5degF (shouldn't have changed more than 0.001 in og by temp conversion charts) but still my o.g. seemed to jump more 0.006. Has anyone done hydrometer readings with dissolved o2 (or other gas?) could the high level of air in my sample have kept my hydrometer high before it stabilized? anything else that could have impacted my reading? any thoughts?

If you check detailed instructions for the use of a hydrometer you will see that it is necessary to wait for a minute or so for everything to come to equilibrium. Roger the comment on bubbles (though this should be more of a concern with fermented or fermenting beer). A vigorous spin of the hydrometer will usually dislodge them.

I understand the minute or so to come to equilibrium, but this was over the course of about an hour (it really took that long for all the foam to die off).

I'm guessing it was just a matter of bubbles rising in solution I wasn't aware of and/or the smattering of foam throwing things off I suppose.

One other thought - over the course of this time it was easy to see floaty break material hanging out in suspension - by the end it was pretty well all settled forming a nice little layer at the bottom. My intuition says this shouldn't change the reading, but can someone confirm? cheers!

One of the tricks to using the Hydro is to fill the jar to a level that causes a slight overflow when you put the Hydro into it. That quickly removes the foam from the jar. Suspended particles can affect your reading if they stick to the Hydrometer otherwise not. Also if your Hydro contacts the side of the jar it can change the readings.

Suspended material that stays in suspension won't effect gravity readings because it is the same density as the liquid it is suspended in. Material which is heavier (or lighter) than than the solution can effect the reading while it is in suspension (i.e. before it settles to the bottom or floats to the top) - if it gets displaced by the body of the instrument it has an effect. If it stays in suspension long enough to be displaced by the body of the instrument it is clearly of a density close to the solution and won't have much of an effect. For example, birdshot would go to the bottom immediately and would not effect the reading because it is not displaced by the hydrometer. Material heavier than the solution which settles out on the shoulder of the hydrometer will obviously effect the reading (as will bubbles). If birdshot stuck to the shoulder of the hydometer it would have an effect.

To the trick of overfilling the hydrometer jar I'll add the suggestion that the foam that remains can be blown off the top with a puff of breath. This gives a clean meniscus for the best reading and no, it does not take an hour for equilibration of surface tension etc.

wouldn't the temperature rise while you were waiting for said foam to dissipate, and would this rise in temperature change your reading?

this was my original thought actually, but as noted in the original post, ambient T was max 70degF, original temp of wort was 65.. according to my research the most this should have changed my reading was 0.001, not the 0.006 that I saw. Of course, what is the precision of this thing, +/- 0.002 I think (?). That combined with the T change would be about enough to account for the change. Add a few rogue bubbles and I think I could nab the culprit(s). Perhaps I should invest in a better precision hydrometer (not at all necessary to make good beer, really.. but I know it's just a matter of time before I 'need' an analytical scale, sterile-grade filters, maybe a GC/mass spec.. )

I think next brew session I'm going to take a few samples and see if I can repeat the phenomenon with a little more knowledge, control, and awareness. cheers!